One Vibration (or One Force, or One Om)
True identity (True name)
"The Divine is not this and it is not that" (neti, neti).
Neti or नेति = न + इति means "not this, not this" that is beyond description.
Guru Arjan Dev Ji agrees with this concept and mentions it in his Salok Sehshritee on page 1359 of the Granth Sahib.
न संखं न चक्रं न गदा न सिआमं ॥
God has no conch-shell, no religious mark, no paraphernalia; he does not have blue skin.
अस्चरज रूपं रहंत जनमं ॥
His Form is Wondrous and Amazing. He is beyond incarnation.
नेत नेत कथंति बेदा ॥
The Vedas say that He is not this, and not that.
ऊच मूच अपार गोबिंदह ॥
The Lord of the Universe is Lofty and High, Great and Infinite.
बसंति साध रिदयं अचुत बुझंति नानक बडभागीअह ॥५७॥
The Imperishable Lord abides in the hearts of the Holy. He is understood, O Nanak, by those who are very fortunate. ||57||